1. Field of the Invention
The present invention relates to refrigerant compressors and, in particular, to an refrigerant compressor using 1,1,1,2-tetrafluoroethane as refrigerant.
2. Description of the Related Art
Generally, in air conditioning apparatus or refrigerators, a refrigeration cycle is used to cool or warm circulating air by heat exchange with a refrigerant moving through a closed, hermetic cycle. The refrigeration cycle has a refrigerant compressor for compressing the refrigerant and circulating the compressed refrigerant.
There are hermetic rotary compressors and semi-hermetic type refrigerant compressor for a car air conditioner and so on as a refrigerant compressor.
Dichlorodifluoromethane (hereafter referred to as CFC 12) or chlorodifluoromethane is used mainly as the refrigerant in the hermetic type refrigerant compressor. As the refrigeration compressor lubricants enclosed in compression mechanism 18, mineral oil of napthene or paraffine is used. These oils have solubility in CFC 12 and chlorodifluoromethane.
The above refrigerant and refrigeration compressor lubricants circulate directly inside of easing 16. There is a need to reduce wear on the various contact surfaces in compression mechanism 18.
Recently, it is recognized that discharge of CFC 12 from the refrigerant destroys the ozone layer, affects the biological system and affects human health. Therefore, CFC 12 is to be gradually reduced in its use and may be prohibited for any use in the future.
In view of the need for a replacement for CFC 12, 1,1,1,2-tetrafluoroethane (hereafter referred to as HFC 134a) and 1,1,2,2-tetrafluoroethane (hereafter referred to as HFC 134) were developed. This shift away from CFC 12, however, has changed the type of lubricants that can be used and affected the construction materials used in the compressor. For example, HFC 134a is hardly dissolved in the conventional mineral oil refrigeration compressor lubricant. Thus, polyalkylene glycol oil, polyether oil, polyester oil or fluorine oil (which all have solubility in the HFC 134a) have been used as the refrigeration compressor lubricant.
However, if the HFC 134a is used as refrigerant and the polyalkylene glycol oil or the polyester oil is used as refrigeration compressor lubricant, when materials such as FC 25 (grey cast iron), S-15C, S-12C (both are carbon steel), SWRCH10A, SWRCH15A (both are carbon steel wire rods for cold heating and cold forging), SCM435H (chromium molybdenum steel), sintering alloy, or stainless steel are used as parts of the compression mechanism, the mechanism is less wear resistant. Then, the problem occurs that the refrigerant compressor may not be operated stably for long time. This change may be explained by the absence of interactions between the lubricant and the iron in the mechanism.
If CFC 12 is used as refrigerant, the iron chloride (FeCl) film having good wear-proof is formed because chlorine (Cl) atoms in CFC 12 reacts with iron (Fe) atoms as metal base. However, if HFC 134a is used as refrigerant, lubricating film such as iron chloride (FeCl) film is not formed because chlorine atoms do not exist in HFC 134a. This is one of the reasons of above problem.
Moreover, refrigeration compressor lubricants that are soluble in HFC 134a are aliphatic compounds rather than cyclic compounds. Aliphatic compounds do not, however, provide an adequate thickness of a lubricating oil film so it is hard to maintain adequate lubrication under hard rubbing conditions. This is one of the reason why wear-resistance is decreased.